Each and every domain that's registered and hosted has quite a lot of DNS records - some of them are set up automatically when you host a domain, others can be created by hand if required. For example, the A record of a domain is its IP address i.e. this record reveals where the website is located; the MX records show where the emails are managed, while through an SRV record you can use a domain for unconventional purposes, for instance a Voice-over-IP service. The ability to create and modify certain records allows you to have different services with different providers if, for instance, your present host provides good web hosting, but has troubles with the email service, or you simply prefer to get a particular service from a specific company. Even though you must be able to set up and edit these records freely and with no limitations as you own a given domain name, many companies charge extra to give you this option.